A significant risk associated with the use of blood products in transfusion medicine is the presence of viruses in such products as whole blood, plasma, platelets, and various blood fractions. A number of chemicals have been identified as viral inactivating agents; their addition to the blood product, sometimes in conjunction with irradiation by visible and/or ultraviolet light, causes viruses to lose their infectivity. For example, methylene blue is added to plasma intended for transfusion. Although methylene blue exhibits effective virucidal activity and is considered generally safe, it nevertheless represents an exogenous component in the plasma with possible long-term adverse effects not yet fully understood. Other viral inactivation agents such as psoralens carry similar risks. One object of the present invention is to offer a method for removing antiviral agents after their virucidal function is completed.
European application 239,859 describes a method that is currently employed to remove lipid soluble process chemicals from biological fluids. It comprises bringing the fluid into contact with a naturally occurring oil, agitating the resultant mixture, separating the phases by sedimentation or centrifugation, decanting the upper lipid phase, and utilizing the residual biological fluid. Aside from the mechanical complexity of this process, it appears applicable only to the removal of lipid soluble process chemicals.
Gel filtration is also known for removing small molecules from blood fractions based on molecular weight differences. Horowitz et al. Transfusion, 25, p. 516-522 (1985)! have described the removal of tri-n-butyl phosphate from anti-hemophilic factor concentrates by chromatography on Sephadex G-25; however, gel chromatography is not a practical method for removing small molecules from plasma and whole blood.
PCT application WO 91/03933 discusses the use of silica gel, modified silica gel, glass beads, and amberlite resins to adsorb methylene blue from plasma. None of the methods presently in use or proposed is particularly attractive for the routine processing of plasma.
A second concern that arises with blood products, including those such as plasma, is their non-homogeneity; blood products commonly include several cell types as well as a variety of molecular components having differing biological activities. Often patients into whom the blood product is to be transfused are only in need of one component, and the other components present in the blood product are not only unnecessary but may even be disadvantageous or harmful. In this respect, leukocytes have come to be regarded as unwanted passengers in transfusions because "once transfused, they may turn upon their host and unleash endogenous pyrogens, cell-associated viruses, or even lethal graft-versus-host disease." see Klein "Wolf in Wolf's Clothing: Is It Time to Raise the Bounty on the Passenger Leukocyte?" Blood 80, 1865-1867 (1992)!. For this reason it is desirable that leukocytes be reduced to the lowest feasible levels. It would therefore be highly desirable to have a method for removing leukocytes from plasma quickly and efficiently. Moreover, there is a need for a simple and effective method for simultaneously removing viral inactivating agents and leukocytes from plasma.
Media and devices for removing leukocytes from red blood cell concentrates, platelet concentrates, and other blood fractions have been described. The media are typically non-woven mats of controlled fiber diameter. They are adequate as components for fabricating a device according to the invention, but media for filtration based primarily on separation by size can be improved by adding ligands for leukocytes, as described in our earlier copending application Ser. No. 08/179,567, abandoned.